1. Field of the Invention
The invention relates to a hybrid vehicle.
2. Description of Related Art
There is known a hybrid vehicle including not only an engine, two rotary electric machines (first rotary electric machine and second rotary electric machine) and a differential unit (power split mechanism) but also a transmission unit (power transmission unit) between the engine and the differential unit.
A vehicle described in International Application Publication No. 2013/114594 is able to switch between motor drive mode (hereinafter, referred to as EV mode) and hybrid mode (hereinafter, referred to as HV mode). In motor drive mode, the engine is stopped, and the power of the second rotary electric machine is used. In hybrid mode, the power of both the engine and the second rotary electric machine is used. A series-parallel mode drive system is employed as an HV drive system. In series-parallel mode, the power of the engine is transmitted to the first rotary electric machine and is used to generate electric power, while part of the power of the engine is also transmitted to drive wheels via the differential unit.
There is also known a series mode drive system as an HV drive system. In the series mode drive system, electric power is generated by using the power of an engine, and a motor is driven by using the generated electric power. In this series mode, the power of the engine is not transmitted to drive wheels.
The vehicle described in International Application Publication No. 2013/114594 is not configured to be able to travel in series mode because the power of the engine is also transmitted to the drive wheels via the differential unit at the time when the power of the engine is transmitted to the first rotary electric machine.
It is conceivable to provide a second path that directly transmits the power of the engine to the first rotary electric machine in addition to a first path that transmits the power of the engine to the first rotary electric machine via the transmission unit (power transmission unit) and the differential unit and then a clutch is provided in the second path. With this configuration, it is possible to select one of the series-parallel mode and the series mode. Specifically, it is possible to select the series-parallel mode by transmitting the power of the engine through the first path (that is, placing the transmission unit provided in the first path in a power transmitting state and releasing the clutch provided in the second path). On the other hand, it is possible to select the series mode by transmitting the power of the engine through the second path (that is, placing the transmission unit provided in the first path in a neutral state and engaging the clutch provided in the second path).
In the above configuration, a mechanical oil pump is connected to any location in a power transmission path from the engine to the drive wheels, and hydraulic pressure for activating the transmission unit provided in the first path and the clutch provided in the second path is allowed to be generated by the mechanical oil pump.
However, for example, in the case where the mechanical oil pump is connected to an input shaft of the transmission unit (power transmission unit), when the engine is stopped, rotation of the input shaft of the transmission unit connected to an output shaft of the engine is also stopped, so it is not possible to activate the mechanical oil pump.